Nine out of 10 cases of gastroenteritis are caused by viruses, which do not respond to antibiotics. Norovirus is a possible cause, but as it typically only lasts 24 hours or so, it is unlikely to be the culprit in the Queen’s case.

The other one case out of 10 is caused by food poisoning, namely Campylobacter or Salmonella bacteria. These can be found in any type of prepared food.

Doctors will be able to tell from lab tests whether the cause was viral or antibacterial, but only after 24 or 48 hours, after which she may well have recovered.

Although gastroenteritis is extremely unpleasant, it is generally a short-lived illness. Her Majesty should suffer no long-term ill-effects.